ProjectSummary ChronicdietaryexposuretoaflatoxinB1(AFB1)isassociatedwithasignificantcancerriskwithincertain populationsinsub-SaharanAfricaandSoutheastAsia,withexceptionallyhighratesofearlyonset hepatocellularcarcinomas(HCCs)thatcanapproach1:1,000/year.HumanexposurestoAFB1comethrough theconsumptionoffoodproductsthatarecontaminatedwiththefungi,Aspergillusflavusorparasiticus.Thus, aflatoxin-associatedHCCsrepresentaglobalhealthissue,withasignificantpercentageofthe~750,000new casesofHCCperyear(in2008)attributedatleastinparttothesedietaryexposures.Concomitantwith ingestionofaflatoxin,thereareadditionalfactorsthatinfluenceHCCinduction,includingchronicinflammation resultingfromhepatitisBandCviralinfectionsandthebalanceofbioactivationanddetoxicationpathways. However,eventhoughdietaryexposurestoaflatoxinsconstitutethesecondlargestenvironmentalriskfactor forcancerdevelopment,onlybehindtobacco-relatedexposures,therearestillsignificantquestionsconcerning themolecularmechanismsdrivingtheunderlyingmutageniceventsandsubsequentcarcinogenesis.The capacityofcellstoinitiateandcompleterepairofpersistentAFB1-inducedDNAadductsdefinesthemutagenic burdeninthetargettissuesandultimatelylimitscellularprogressiontocancer.Althoughthenucleotide excisionrepairpathwayhasbeenpreviouslydemonstratedtocorrectthetwomajorAFB1DNAadducts, evidenceispresentedhereinthatdemonstratesthatthebaseexcisionrepair(BER)pathwayisveryefficientin therecognitionandremovalofthehighlymutagenicAFB1-Fapy-dGadduct.Thishasbeendemonstrated through1)biochemicalDNAincisionassaysusingsite-specificallymodifiedoligodeoxynucleotides,2) measurementsofhighlyelevatedlevelsofAFB1-Fapy-dGadductsinBER-deficientmicerelativetowild-type mice,and3)elevatedAFB1-inducedcarcinogenesisinBER-deficientmiceversuscontrolBER-proficientmice. Further,DNApolymerase ?hasbeenshowntoberesponsiblefortheGtoTtransversionsignatureassociated withaflatoxinexposure.Usingsite-specificallymodifiedoligodeoxynucleotidesandknockoutmousemodels, thisapplicationproposestoestablishthemolecularmechanismsbywhichDNArepairlimitsAFB1-induced mutagenesisandcarcinogenesis.Additionally,theinvivoroleofpol?inmodulatingtheoutcomeofreplication pastAFB1adductswillbeinvestigated.Thesestudieshavedirecthumanhealthrelevanceinregardto understandingaglobalenvironmentalhealthproblembyidentifyinggenesandbiochemicalpathways previouslynotrecognizedasgermanetoAFB1-inducedcarcinogenesis.Additionally,thefundamental mechanisticinsightsderivedfromtheproposedanalyseswillguidehumanepidemiologicalandinterventional investigationsoftheroleofDNArepairinreducingearlyonsetHCCs.